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When scaling max/min settings are changed, internally they are converted to a ratio using the max turbo 1 core turbo frequency. This works fine when 1 core max is same irrespective of the core. But under Turbo 3.0, this will not be the case. For example: Core 0: max turbo pstate: 43 (4.3GHz) Core 1: max turbo pstate: 45 (4.5GHz) In this case 1 core turbo ratio will be maximum of all, so it will be 45 (4.5GHz). Suppose scaling max is set to 4GHz (ratio 40) for all cores ,then on core one it will be = max_state * policy->max / max_freq; = 43 * (4000000/4500000) = 38 (3.8GHz) = 38 which is 200MHz less than the desired. On core2, it will be correctly set to ratio 40 (4GHz). Same holds true for scaling min frequency limit. So this requires usage of correct turbo max frequency for core one, which in this case is 4.3GHz. So we need to adjust per CPU cpu->pstate.turbo_freq using the maximum HWP ratio of that core. This change uses the HWP capability of a core to adjust max turbo frequency. But since Broadwell HWP doesn't use ratios in the HWP capabilities, we have to use legacy max 1 core turbo ratio. This is not a problem as the HWP capabilities don't differ among cores in Broadwell. We need to check for non Broadwell CPU model for applying this change, though. Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com> Cc: 4.6+ <stable@vger.kernel.org> # 4.6+ Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.